1. Field of the Invention
This invention relates to apparatus for forming casting molds and, more particularly, to a structure for controlling delivery of sand into a flask to define such a mold.
2. Background Art
A known metal forming process employs a sand mold into which molten metal is poured and cast. Typically, a pattern, representing a desired part configuration, is situated within a flask or mold. Sand is tamped or packed about the pattern to reproduce its contour, whereupon the pattern is removed. The molten metal introduced to the mold assumes the shape of the cavity.
It is known to form the patterns from STYROFOAM, which is economically more feasible than the use of wood patterns, which is common. The STYROFOAM pattern has the further advantage that it will exhaust as a gas through a system of risers and gates upon introduction of the molten material to the mold, and will not leave a residue that might compromise the quality of the casting.
To assure that the sand completely duplicates the contour of the pattern and does not bridge or hang up, which might prevent its passage into tight crevices, one practice in the art has been to compress the sand against the pattern. One such apparatus that operates in this manner is shown in U.S. Pat. No. 3,234,601, to Hatch et al. In Hatch et al a pneumatically operated squeeze ram is used to compact the mold.
The principal drawback with this type of mold formation is that it is impractical where a delicate pattern such as one having a slender protrusion or finger, is used or STYROFOAM makes up the pattern. The pattern might bend, curl and/or be destroyed under the impact of the compressing cylinder. The use of a ceramic coating over the STYROFOAM to enhance its stability alleviates but does not eliminate the problem of pattern alteration. Any change in the pattern results in an inferior and/or unacceptable casting.
An alternative to the compression type mold formation is the provision of a vibratory apparatus that is operable to vibrate the flask and pattern and cause an even distribution and compaction of sand around the pattern. While this particular process is generally acceptable, one still contends with the problem of pattern breakage upon the sand encountering the pattern.
In a typical apparatus, a hopper is disposed above the flask and associated pattern. Generally, in most apparatus, the sand rains freely over the pattern. With nothing to interrupt the hopper flow, the incoming sand may break off portions of the pattern. Reduction of the flow rate to the flask, while preventing damage to certain delicate portions of the pattern, slows the entire operation and results in a bottleneck in the assembly line. The economic consequences are apparent.
The present invention is specifically directed to overcoming the above enumerated deficiencies in a novel and simple manner.